Numerous herbicides have recently come to be used in the cultivation of agricultural crops, and have contributed to reduced labor for farmers and improved productivity of agricultural crops. Numerous herbicides are also used practically in the cultivation of field and paddy rice.
However, there is considerable diversity in the species of weeds, the germination and growth periods of each species of weed are not uniform, and the growth of perennial weeds extends over a long period of time. Consequently, it is extremely difficult to control all weeds with a single spraying of herbicide.
Early to mid-term one-shot herbicides have been shown to be effective for paddy rice by treating during the second to third leaf stage of paddy weeds (generic term for Echinochloa oryzicola, Echinochloa crus-galli var. crus-galli, Echinochloa crus-galli var. formosensis, Echinochloa crus-galli var. praticola and Echinochloa crus-galli var. caudata), and major weeds can be controlled by a single treatment (see Non-Patent Document 1). However, it is extremely difficult to control paddy weeds that have grown to the 3.5 leaf stage or more with early to mid-term one-shot herbicides currently in practical use, and the control of paddy weeds in the third leaf stage and control of paddy weeds in the 3.5 leaf stage are technically completely different.
Moreover, maintaining herbicidal effects (residual activities) over a long period of time is important in terms of reducing spraying of agricultural chemicals, saving on labor and curtailing costs, and is considered to be an essential area of performance for early to mid-term one-shot herbicides.
In addition, acetolactate synthase (ALS) inhibitors have come to be widely used in recent years, and weeds exhibiting resistance to ALS inhibitors have become a problem. There are few herbicides demonstrating adequate efficacy against ALS inhibitor-resistant biotypes of the perennials of Sagittaria trifolia and Sagittaria pygmeae. In addition, examples of perennial weeds that have caused problems in recent years include Eleocharis kuroguwai, Scirpus planiculmis and Scirpus nipponicus, while examples of annuals include Aeschynomene indica, Leptochloa chinensis and Murdannia keisak, and there are few herbicides that demonstrate adequate efficacy against these difficult-to-control weeds.
On the other hand, numerous pyrazole derivatives are used practically as herbicides, and although pyrazole derivatives such as 4-(2,4-dichlorobenzoyl)-1,3-dimethyl-5-pyrazolyl p-toluenesulfonate (common name: “Pyrazolate”), 2-[4-(2,4-dichlorobenzoyl)-1,3-dimethylpyrazol-5-yloxy]acetophenone (common name: “Pyrazoxyfen”) or 2-[4-(2,4-dichloro-m-toluoyl)-1,3-dimethylpyrazol-5-yloxy]-4′-methylac etophenone (common name: Benzofenap”) are widely used, their registered application range for paddy weeds in Japan when used alone is up to the 1.5 leaf stage, and although these pyrazole derivatives are effective against a wide range of weeds, the efficacy thereof is not always adequate against paddy weeds of higher leaf stages.
In addition, although Compound 73 of Example 4 described in Patent Document 1 in the form of 1-(3-chloro-4,5,6,7-tetrahydropyrazolo[1,5-a]pyridin-2-yl) 5-[methyl(p rop-2-ynyl)amino]pyrazole-4-carbonitrile (common name: “Pyraclonil”) is effective against a wide range of weeds, its efficacy against paddy weeds of higher leaf stages is inadequate, and the registered application range in Japan against paddy weeds when using this herbicide alone is up to the 1.5 leaf stage.